The invention is a regenerator that is more particularly described as a regenerator for a fiber optic transmission system.
Exploratory research and development of optical devices and components have progressed sufficiently during recent years that a fiber optic digital transmission system now can be built and operated. Multimode and single mode glass fibers can transmit optical signals over long distances. In new glass fibers, light losses are less than 5 decibels per kilometer for wavelengths between 800 nanometers and 1100 nanometers. Some single mode borosilicate fibers have a minimum loss of 2.2 decibels per kilometer at 850 and 1020 nanometers and a dispersion of approximately 0.4 nanoseconds per kilometer. Fibers with the above characteristics are useful for digital communications systems. A moderate pulse rate optical system can be used economically for telephone exchange trunking in congested metropolitan areas having a large and growing traffic cross section.
In the glass fibers, optical pulses are attenuated as they proceed through any fiber. Along any fairly long communications route, it is necessary to regenerate the optical pulse stream for insuring accurate communication from one end of the system to the other.
In the prior art, most of the basic optical regenerator circuitry is similar to the circuitry employed in commercial pulse code modulation systems which transmit electrical pulses over copper wire pairs or coaxial cables. In the optical regenerators, optical elements such as avalanche photodiodes and lasers have been inserted for converting optical power to electrical signals and vice versa.
Also in the prior art, phase-lock loops have been used to extract timing information from an input pulse stream; however, those phase-lock loops use narrow range acquisition requiring expensive crystal control.
Additionally in the prior art, an injection laser is operated in response to a feedback control circuit which senses the output optical power from the laser and attempts to maintain a constant average optical output power. Occasionally, many time slots pass wherein no pulses are applied to the input of such a laser. The prebias current rises to maintain constant output power. Subsequently irreversible damage can occur to the laser when pulses are applied again.
Therefore, it is an object to provide an improved regenerator for an optical transmission system.
It is another object to provide a regenerator for a moderately high pulse rate and low error rate optical transmission system.
It is a further object to provide an optical regenerator having a wide dynamic range, i.e., operable for a wide range of input optical powers.
It is a still further object to provide an optical regenerator for producing substantially constant amplitude output pulses of light throughout a long lifetime.